It will be appreciated that the invention has applications with respect to improvements in electronic packaging may be suitable for many applications. However, the present invention has some unique features which maximize utilization of space within an implantable medical device.
Implantable medical devices of the type having electrical circuit components are well known in the medical arts. In one particularly common form, the implantable device comprises a pacemaker having an appropriate electrical power supply and related control circuitry for use in electrically stimulating a patient muscle, such as the heart. Such a pacemaker commonly includes an hermetically sealed case or housing within which the power supply and control circuitry are protectively encased, in combination with one or more conductive pacemaker leads extending from the housing to the selected muscle structure within the patient.
Signals into and out of the circuitry within the housing are coupled through the housing by means of feedthrough terminals of various types known in the art. Examples of such a cardiac pacemaker may be found in commonly assigned U.S. Pat. No. 5,282,841 to Szyszkowski.
As is apparent from the Szyszkowski patent, the size of the housing is dependent upon that required to house both the battery and the electronic circuit constituting the pulse generator. A major factor which drives the electronic package design is the need to fit large, generally rectangular or cylindrical components into a physiologically-shaped, curved housing. Of course, efforts are continually being made to minimize the size of the housing while maximizing the effectiveness of the device. To a large extent the size of the battery is dependent upon the anticipated lifetime, as well as cost factors of the type of battery employed. In addition to improvements in batteries, great strides have been made in component packaging which greatly affects the size of the electronic circuit employed. For example, the circuitry illustrated in the U.S. Pat. No. 4,127,134 to Ushakoff shows discrete components as opposed to integrated circuits or chips as employed, more recently, in the U.S. Pat. No. 4,616,655 to Weinberg et al. The Weinberg et al. patent discloses a microprocessor based pulse generator for use as a cardiac pacemaker and utilizes integrated circuits including active chips, such as microprocessors and other active circuits, together with passive chips, such as chip resistors and chip capacitors. The use of such integrated circuits requires less space than discrete components and, thus, provides a reduction in the size necessary for the circuitry employed in such an implantable pulse generator.
As disclosed in Weinberg et al., the pulse generator includes an implantable sealed housing of biocompatible material and which contains a power supply and a pulse generator circuit powered by the supply for providing stimulation pulses. The electronic pulse generator circuit includes a plurality of semiconductor chips including active chips and passive chips together with chip carrier means for carrying the semiconductor chips in a single structure. The active chips are mounted in a hermetically sealed cavity located in one of the major surfaces of the assembly and the passive chips are mounted to bonding pads located on the other major surface. The passive chips and active chips are electrically interconnected by way of a network of metallized paths located on the various ceramic layers together with vertically extending electrically conductive vias which extend through various of the layers to the passive chip mounting pads. Various of these metallized paths also extend laterally outward to metallized edges which extend along the peripheral edge of the assembly to I/O mounting pads on the bottom surface of the assembly so that the assembly may be electrically and physically mounted to a mother board or a substrate.
The present invention represents a continuation of the improvements begun by Weinberg at al. and it was in light of the foregoing that the present invention was conceived and has now been reduced to practice.